Linear or branched structure? Probing molecular architectures of fullerene-styrene copolymers by size exclusion chromatographs with online right-angle laser-light scattering and differential viscometric detectors

The poly(C₆₀-co-styrene)s prepared by radical copolymerizations of C₆₀ and styrene in bulk were characterized by multiple-detector size-exclusion chromatographs consisting of a refractometer, a differential viscometer, and/or a right-angle laser-light scattering photometer. The multidetector systems enabled the determinations of reliable, absolute molecular weights of the copolymers. The plots of intrinsic viscosity vs. molecular weight and radius of gyration vs. molecular weight offered valuable information about the molecular architectures of the copolymers. The slopes of the plots reveal that the structure of the copolymer changes with its C₆₀ content: the copolymer with a low C₆₀ content of 0.58 wt% possesses a linear structure, whereas its conger with a high C₆₀ content of 1.14 wt% possesses a branched structure.     

Studies on the hydrodynamic and heat transfer in a vapor-liquid-solid flow boiling system with a CCD measuring technique

The vapor-liquid-solid (V-L-S) flow boiling evaporator has the features of fouling preventing and heat-transfer enhancing. However, the mechanisms of flow and heat-transfer are still not well understood due to the system complex and the limitation of the measuring methods due to the characteristic of opaque of the system in practice. In this paper, a charge coupled device (CCD) measuring system is developed to investigate the hydrodynamic characteristics including the axial profiles of solid holdup and of solid velocity in a V-L-S three-phase natural circulating flow boiling system. The CCD measuring technique makes the three-phase qualitative observation and quantitative research possible. The heat-transfer characteristic of this system is also studied. The main results are as follows. The distributions of solid holdup and velocity are not uniform along the axial direction of the heating tube and both in liquid-solid two-phase region and in V-L-S three-phase region; however, the particle velocity in V-L-S three-phase region is much higher than that in liquid-solid two-phase region in heating tube. When increasing the heat flux, the solid holdup first increases and then decreases and the solid velocity gradually increases in heating tube. But in circulating tube, both the solid holdup and the solid velocity gradually increase. With the increase of the volume of added solid particles, the measured local solid holdup increases in both tubes; however, the variation of the solid velocity with the increase of the solid particles shows a characteristic of the wave and the general tendency is climbing for both tubes. The solid particles holdup in heating tube is always larger than that in circulating tube and the solid velocity in heating tube is lower than that in circulating tube. The presence of solid particles enhances the boiling evaporation process. The heat-transfer coefficient of the system increases with the increase of the heat flux and the volume of added solid particles. These research results provide some valuable references for the academic interest and for the industry application of this fouling preventing and heat-transfer enhancing installation.     

A Novel Temperature Stable Microwave Dielectric Ceramic with Garnet Structure: Sr2NaMg2V3O12

A garnet vanadate ceramic Sr₂NaMg₂V₃O₁₂ was prepared by the conventional solid‐state route, and the sinterability, microwave dielectric properties, and its chemical compatibility with Ag electrodes were investigated. Sr₂NaMg₂V₃O₁₂ sample could be well sintered at 900°C for 4 h with a relative density of 96.1%. X‐ray diffraction data showed that Sr₂NaMg₂V₃O₁₂ ceramics crystallized into a cubic garnet structure with a space group Ia‐3d over the sintering temperature range (830°C–930°C). The Sr₂NaMg₂V₃O₁₂ ceramic sintered at 900°C obtained the optimum microwave dielectric properties with a relative permittivity of 11.7, a Q×f of 37 950 GHz (at 11.0 GHz), and a almost zero τ_f value of ?2.9 ppm/°C. Chemical compatibility experiments showed no reaction between Sr₂NaMg₂V₃O₁₂ ceramics and Ag electrodes.     

Chelation of chitosan derivatives with zinc ions. II. Association complexes of Zn2+ onto O,N‐carboxymethyl chitosan

The chelation of zinc ions onto O,N‐carboxymethyl chitosan (ONCMCh) was characterized using a Fourier transform infrared (FTIR) spectrophotometer and a scanning electron microscope (SEM). From the FTIR spectra, little change in the absorption intensities and frequencies at 3300–3600 cm⁻¹ of Zn²⁺ ONCMCh chelated specimens suggested that  OH and  NH₂ groups were not participating in the chelation reaction. The absence of absorption bands at 1755–1700 cm⁻¹ suggested that the carboxyl group CO was not ionized, and the ionized CO bands were observed at 1400–1600 cm⁻¹ for chelated specimens. Thus, the chelation sites took place at the carboxyl group rather than at the  OH and NH₂ groups. It also confirmed that water‐insoluble chelates, which were formed through the Zn O and Zn N bonds, presented a tetrahedral structure. The water‐soluble complexes where zinc ions connected with oxygen of CO and water molecules were only due to electron attraction. Formation of different microstructures on the surfaces, as revealed by SEM, provided evidence to distinguish different chelating mechanisms between water‐soluble and water‐insoluble complexes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1476–1485, 2001     

气相色谱法测定三氯乙酰氯的含量

介绍了用无水乙醇作衍生反应试剂,采用5％PEG－12000填充柱和PID检测器,对三氯乙酰氯的衍生物进行分离,以草酸二乙酯为内标物,进行了内标法定量,实现了三氯乙酰氯的简便,快速,无腐蚀气相色谱分析。     

三氟乙烯合成工艺及催化剂研究进展

在三氟乙烯的制备工艺中,存在的主要问题是催化剂转化率低、选择性差、寿命短、容易失活,所以制备高活性、不易失活、长寿命的催化剂成为行业发展的主要趋势。对三氟乙烯的性质及用途进行了简要介绍。根据初始原料的不同分别综述了两种不同工艺使用的催化剂,并对现有的催化剂优缺点进行了讨论。     

压力式喷雾并流干燥磷酸—铵的粉料物性及其生产的特殊要求

1999年元月,我厂首次启动粉状磷酸一铵生产线,采用南化集团设计院设计的压力式喷雾并流干燥直接出料流程,生产中遇到了一些问题,我们采取了一系措施,生产已比较稳定,现就生产中出现的现象,分析并流干燥磷酸一铵的粉料物性及生产中的特殊要求。     

浅谈改变氨压机排气量来调节制冷量

阐述环境温度对制冷量的影响以及在实际生产中如何通过改变现有氨压机的排气量,来调节制冷量、适应生产需要。     

钼酸盐在高氯离子溶液中的协同缓蚀作用

采用极化曲线、旋转挂片等方法研究了钼酸盐与有机膦酸、正磷酸盐和锌盐等缓蚀剂在低硬度、高氯离子的水质条件下的缓蚀作用。结果表明 ,几种缓蚀剂之间具有良好的协同效应 ,其中锌盐的作用最为明显。     

Water-Based Gelcasting of Surface-Coated Silicon Nitride Powder

A layer of Y₂O₃–Al₂O₃, used as a sintering aid, was coated onto the surface of Si₃N₄ particles by the precipitation of inorganic salts from a water-based solution containing Al(NO₃)₃, Y(NO₃)₃, and urea. The electrokinetic and colloidal characteristics of the Si₃N₄ powder were changed significantly by the coating layer. As a result, dispersion of the Y₂O₃–Al₂O₃-coated Si₃N₄ powder was significantly greater than that of the original powder. Furthermore, the Y₂O₃–Al₂O₃ coating layer prevented the hydrogen-gas-discharging problem that occurred during gelcasting of the original Si₃N₄ powder because of reaction between the uncoated powder and the basic aqueous solution in suspension. Surface coating, as well as the gelcasting process, significantly improved the microstructure, room-temperature bending strength, and Weibull modulus of the resulting ceramic bodies.